Orbital-FFLO state in a chain of high spin ultracold atoms

TL;DR

This paper investigates the phase diagram of a one-dimensional high-spin ultracold atom system with two orbitals, revealing competing orders including density waves, spin fluctuations, and exotic FFLO-like pairing, with phase transitions near resonances.

Contribution

It provides the first analysis of the phase diagram of high-spin two-orbital ultracold atoms in 1D, identifying competing orders and phase transitions driven by tunable interactions.

Findings

Identification of three competing orders: density wave, spin density, and FFLO-like pairing.

Divergence of compressibility indicating phase separation near resonances.

Observation of power-law decay in correlations for different phases.

Abstract

Recent experiments with Yb-173 and Sr-87 isotopes provide new possibilities to study high spin two-orbital systems. Within these experiments part of the atoms are excited to a higher energy metastable electronic state mimicking an additional internal (orbital) degree of freedom. The interaction between the atoms depends on the orbital states, therefore four different scattering channels can be identified in the system characterized by four independent couplings. When the system is confined into a one-dimensional chain the scattering lengths can be tuned by changing the transverse confinement, and driven through four resonances. Using the new available experimental data of the scattering lengths we analyze the phase diagram of the one-dimensional system as the couplings are tuned via transverse confinement, and the populations of the two orbital states are changed. We found that three orders compete showing power law decay: a state with dominant density wave fluctuations, another one with spin density fluctuations, and a third one characterized by exotic Fulde-Ferrell-Larkin-Ovchinnikov-like pairs consisting one atom in the electronic ground state and one in the excited state. We also show that sufficiently close to the resonances the compressibility of the system starts to diverge indicating that the emerging order is unstable and collapses to a phase separated state with a first order phase transition.